This invention relates generally to heat exchangers and, more particularly, to two-phase refrigerant distribution for multipass parallel tube coils. Two-phase flow of refrigerant needs to be uniformly redistributed between passes into several parallel tubes. The refrigerant from the first pass generally exits into a collection header after which it then passes along the header to the entrance area of the second pass. Partly, because of the dissipation of heat and pressure in the first pass, significant mal-distribution of liquid refrigerant tends to occur in the second and subsequent passes.
The above described phenomenon is particularly true in the case of parallel flow heat exchangers that use flat tubes with microchannels, which are widely used in automotive air conditioning as condensers. The tubes are laid in a horizontal direction and are attached to common headers. When operating as a condenser, the heat exchanger performs satisfactorily, but when the heat exchanger is used as an evaporator, the mal-distribution of two-phase refrigerant occurs as described above.